Bimodal Polyethylene Resins and Pipes Produced Therefrom

ABSTRACT

Disclosed herein are ethylene-based polymers generally characterized by a density of at least 0.94 g/cm 3 , a high load melt index from 4 to 20 g/10 min, a zero-shear viscosity at 190° C. from 20,000 to 400,000 kPa-sec, and a relaxation time at 190° C. from 225 to 3000 sec. These ethylene polymers can be produced by peroxide-treating a broad molecular weight distribution Ziegler-catalyzed resin, and can be used in large diameter, thick wall pipes and other end-use applications.

FIELD OF THE INVENTION

The present disclosure generally relates to the peroxide treatment of apolyolefin base resin to produce a high molecular weight ethylenepolymer, and the subsequent use of the ethylene polymer to produce largediameter, thick wall pipes where slump or sag can be a limiting factor.

BACKGROUND OF THE INVENTION

Polyolefins such as high density polyethylene (HDPE) homopolymer andlinear low density polyethylene (LLDPE) copolymer can be produced usingvarious combinations of catalyst systems and polymerization processes.Metallocene-based catalyst systems can, for example, produce ethylenepolymers having good impact strength, tear resistance, and opticalproperties, but often at the expense of poor extrusion processabilityand melt strength. Chromium-based catalyst systems can, for example,produce ethylene polymers having good extrusion processability andpolymer melt strength in certain pipe applications, typically due totheir broad molecular weight distribution (MWD).

However, it can be difficult for metallocene-based and chromium-basedcatalyst systems to produce polymers that can be successfully extrudedinto large diameter and thick wall pipe products. Accordingly, it is tothis end that the present invention is generally directed.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify required oressential features of the claimed subject matter. Nor is this summaryintended to be used to limit the scope of the claimed subject matter.

The present invention generally relates to ethylene polymers (e.g.,comprising an ethylene/α-olefin copolymer) characterized by a density ofat least about 0.94 g/cm³, a HLMI (I₂₁) in a range from about 4 to about20 g/10 min, a zero-shear viscosity (η₀) at 190° C. in a range fromabout 20,000 to about 400,000 kPa-sec, and a relaxation time (τ_(η)) at190° C. in a range from about 225 to about 3000 sec. For example, theethylene polymer can have a density in a range from about 0.94 to about0.96 g/cm³, a HLMI (I₂₁) in a range from about 4 to about 18 g/10 min, azero-shear viscosity (110) at 190° C. in a range from about 30,000 toabout 300,000 kPa-sec, and a relaxation time (τ_(η)) at 190° C. in arange from about 250 to about 2500 sec. These ethylene polymers can beused to produce various articles of manufacture, such as large diameter,thick wall pipes.

These ethylene polymers can be produced, for instance, by a processcomprising contacting a base resin (e.g., an ethylene copolymer) with aperoxide compound to produce the ethylene polymer. In some aspects, thecontacting step can comprise a step of melt processing a blend ormixture of the base resin and the peroxide compound at a suitable meltprocessing temperature, and often, the amount of peroxide groups rangesfrom about 60 to about 200 ppm by weight of the base resin. Generally,the base resin can be characterized by a density of at least about 0.94g/cm³, a HLMI (I₂₁) in a range from about 4 to about 25 g/10 min, a Mwin a range from about 200,000 to about 500,000 g/mol, and a ratio ofMw/Mn in a range from about 12 to about 40.

Both the foregoing summary and the following detailed descriptionprovide examples and are explanatory only. Accordingly, the foregoingsummary and the following detailed description should not be consideredto be restrictive. Further, features or variations may be provided inaddition to those set forth herein. For example, certain aspects andembodiments may be directed to various feature combinations andsub-combinations described in the detailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a plot of the molecular weight distribution of theethylene polymer of Example C.

FIG. 2 presents a dynamic rheology plot (viscosity versus shear rate) at190° C. for the pipe of Example A and the ethylene polymers of ExamplesB-C.

DEFINITIONS

To define more clearly the terms used herein, the following definitionsare provided. Unless otherwise indicated, the following definitions areapplicable to this disclosure. If a term is used in this disclosure butis not specifically defined herein, the definition from the IUPACCompendium of Chemical Terminology, 2nd Ed (1997), can be applied, aslong as that definition does not conflict with any other disclosure ordefinition applied herein, or render indefinite or non-enabled any claimto which that definition is applied. To the extent that any definitionor usage provided by any document incorporated herein by referenceconflicts with the definition or usage provided herein, the definitionor usage provided herein controls.

Herein, features of the subject matter are described such that, withinparticular aspects, a combination of different features can beenvisioned. For each and every aspect and/or feature disclosed herein,all combinations that do not detrimentally affect the articles/pipes,compositions/polymers, and/or processes/methods described herein arecontemplated with or without explicit description of the particularcombination. Additionally, unless explicitly recited otherwise, anyaspect and/or feature disclosed herein can be combined to describeinventive features consistent with the present disclosure.

While articles/pipes, compositions/polymers, and processes/methods aredescribed herein in terms of “comprising” various components or steps,the articles/pipes, compositions/polymers, and processes/methods canalso “consist essentially of” or “consist of” the various components orsteps, unless stated otherwise.

The terms “a,” “an,” “the,” etc., are intended to include pluralalternatives, e.g., at least one, unless otherwise specified. Forinstance, the disclosure of “an additive” or “a comonomer” is meant toencompass one, or mixtures or combinations of more than one, additive orcomonomer, respectively, unless otherwise specified.

Generally, groups of elements are indicated using the numbering schemeindicated in the version of the periodic table of elements published inChemical and Engineering News, 63(5), 27, 1985. In some instances, agroup of elements can be indicated using a common name assigned to thegroup; for example, alkali metals for Group 1 elements, alkaline earthmetals for Group 2 elements, transition metals for Group 3-12 elements,and halogens or halides for Group 17 elements.

For any particular compound disclosed herein, the general structure orname presented is also intended to encompass all structural isomers,conformational isomers, and stereoisomers that can arise from aparticular set of substituents, unless indicated otherwise. Thus, ageneral reference to a compound includes all structural isomers unlessexplicitly indicated otherwise; e.g., a general reference to pentaneincludes n-pentane, 2-methyl-butane, and 2,2-dimethylpropane, while ageneral reference to a butyl group includes an n-butyl group, asec-butyl group, an iso-butyl group, and a tert-butyl group.Additionally, the reference to a general structure or name encompassesall enantiomers, diastereomers, and other optical isomers whether inenantiomeric or racemic forms, as well as mixtures of stereoisomers, asthe context permits or requires. For any particular formula or name thatis presented, any general formula or name presented also encompasses allconformational isomers, regioisomers, and stereoisomers that can arisefrom a particular set of substituents.

The term “polymer” is used herein generically to include olefinhomopolymers, copolymers, terpolymers, and the like, as well as alloysand blends thereof. The term “polymer” also includes impact, block,graft, random, and alternating copolymers. A copolymer is derived froman olefin monomer and one olefin comonomer, while a terpolymer isderived from an olefin monomer and two olefin comonomers. Accordingly,“polymer” encompasses copolymers and terpolymers derived from any olefinmonomer and comonomer(s) disclosed herein. Similarly, the scope of theterm “polymerization” includes homopolymerization, copolymerization, andterpolymerization. Therefore, an ethylene polymer would include ethylenehomopolymers, ethylene copolymers (e.g., ethylene/α-olefin copolymers),ethylene terpolymers, and the like, as well as blends or mixturesthereof. Thus, an ethylene polymer encompasses polymers often referredto in the art as LLDPE (linear low density polyethylene) and HDPE (highdensity polyethylene). As an example, an olefin copolymer, such as anethylene copolymer, can be derived from ethylene and a comonomer, suchas 1-butene, 1-hexene, or 1-octene. If the monomer and comonomer wereethylene and 1-hexene, respectively, the resulting polymer can becategorized an as ethylene/1-hexene copolymer. The term “polymer” alsoincludes all possible geometrical configurations, unless statedotherwise, and such configurations can include isotactic, syndiotactic,and random symmetries. Moreover, the “polymers” disclosed herein (e.g.,an ethylene polymer, a base resin) also can be referred to herein as“polymer compositions.”

The term “contacting” is used herein to refer to materials or componentswhich can be blended, mixed, slurried, dissolved, reacted, treated,compounded, or otherwise contacted or combined in some other manner orby any suitable method. The materials or components can be contactedtogether in any order, in any manner, and for any length of time, unlessotherwise specified.

Although any methods, devices, and materials similar or equivalent tothose described herein can be used in the practice or testing of theinvention, the typical methods, devices, and materials are hereindescribed.

All publications and patents mentioned herein are incorporated herein byreference for the purpose of describing and disclosing, for example, theconstructs and methodologies that are described in the publications,which might be used in connection with the presently describedinvention.

Several types of ranges are disclosed in the present invention. When arange of any type is disclosed or claimed, the intent is to disclose orclaim individually each possible number that such a range couldreasonably encompass, including end points of the range as well as anysub-ranges and combinations of sub-ranges encompassed therein. As arepresentative example, the high load melt index (HLMI) of the ethylenepolymer can be in certain ranges in various aspects of this invention.By a disclosure that the HLMI can be in a range from about 4 to about 18g/10 min, the intent is to recite that the HLMI can be any value withinthe range and, for example, can be equal to about 4, about 5, about 6,about 7, about 8, about 9, about 10, about 11, about 12, about 13, about14, about 15, about 16, about 17, or about 18 g/10 min. Additionally,the HLMI can be within any range from about 4 to about 18 g/10 min (forexample, from about 6 to about 14 g/10 min), and this also includes anycombination of ranges between about 4 and about 18 g/10 min (forexample, the HLMI can be in a range from about 4 to about 8 g/10 min, orfrom about 10 to about 16 g/10 min). Likewise, all other rangesdisclosed herein should be interpreted in a manner similar to thisexample.

The term “about” means that amounts, sizes, formulations, parameters,and other quantities and characteristics are not and need not be exact,but can be approximate and/or larger or smaller, as desired, reflectingtolerances, conversion factors, rounding off, measurement errors, andthe like, and other factors known to those of skill in the art. Ingeneral, an amount, size, formulation, parameter or other quantity orcharacteristic is “about” or “approximate” whether or not expresslystated to be such. The term “about” also encompasses amounts that differdue to different equilibrium conditions for a composition resulting froma particular initial mixture. Whether or not modified by the term“about,” the claims include equivalents to the quantities. The term“about” can mean within 10% of the reported numerical value, preferablywithin 5% of the reported numerical value.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed generally to high molecular weightethylene-based polymers having excellent melt strength and a broadmolecular weight distribution. Articles of manufacture, such as largediameter and thick wall pipes, can be produced from these ethylene-basedpolymers without slump or sag, and at commercially-acceptable productionrates.

Ethylene Polymers

Generally, the polymers disclosed herein are ethylene-based polymers, orethylene polymers, encompassing homopolymers of ethylene as well ascopolymers, terpolymers, etc., of ethylene and at least one olefincomonomer. Comonomers that can be copolymerized with ethylene often canhave from 3 to 20 carbon atoms in their molecular chain. For example,typical comonomers can include, but are not limited to, propylene,1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and the like, orcombinations thereof. In an aspect, the olefin comonomer can comprise aC₃-C₁₈ olefin; alternatively, the olefin comonomer can comprise a C₃-C₁₀olefin; alternatively, the olefin comonomer can comprise a C₄-C₁₀olefin; alternatively, the olefin comonomer can comprise a C₃-C₁₀α-olefin; alternatively, the olefin comonomer can comprise a C₄-C₁₀α-olefin; alternatively, the olefin comonomer can comprise 1-butene,1-hexene, 1-octene, or any combination thereof or alternatively, thecomonomer can comprise 1-hexene. Typically, the amount of the comonomer,based on the total weight of monomer (ethylene) and comonomer, can be ina range from about 0.01 to about 20 wt. %, from about 0.1 to about 10wt. %, from about 0.5 to about 15 wt. %, from about 0.5 to about 8 wt.%, or from about 1 to about 15 wt. %.

In one aspect, the ethylene polymer of this invention can comprise anethylene/α-olefin copolymer, while in another aspect, the ethylenepolymer can comprise an ethylene homopolymer, and in yet another aspect,the ethylene polymer of this invention can comprise an ethylene/α-olefincopolymer and an ethylene homopolymer. For example, the ethylene polymercan comprise an ethylene/1-butene copolymer, an ethylene/1-hexenecopolymer, an ethylene/1-octene copolymer, an ethylene homopolymer, orany combination thereof; alternatively, an ethylene/1-butene copolymer,an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or anycombination thereof; or alternatively, an ethylene/1-hexene copolymer.

Ethylene polymers disclosed herein can be produced using a Ziegler-Nattacatalyst system, and these polymers have a unique combination ofprocessability and physical properties needed for the production oflarge diameter pipes with thick walls, where excessive slump or sag canbe an issue. An illustrative and non-limiting example of an ethylenepolymer (e.g., comprising an ethylene copolymer) of the presentinvention can have a density of at least about 0.94 g/cm³, a HLMI (I₂₁)in a range from about 4 to about 20 g/10 min, a zero-shear viscosity(η₀) at 190° C. in a range from about 20,000 to about 400,000 kPa-sec,and a relaxation time (τ_(η)) at 190° C. in a range from about 225 toabout 3000 sec. Another illustrative and non-limiting example of anethylene polymer (e.g., comprising an ethylene copolymer) of the presentinvention can have a density in a range from about 0.94 to about 0.96g/cm³, a HLMI (I₂₁) in a range from about 4 to about 18 g/10 min, azero-shear viscosity (η₀) at 190° C. in a range from about 30,000 toabout 300,000 kPa-sec, and a relaxation time (τ_(η)) at 190° C. in arange from about 250 to about 2500 sec. These illustrative andnon-limiting examples of ethylene polymers consistent with the presentinvention also can have any of the polymer properties listed below andin any combination, unless indicated otherwise.

The densities of ethylene-based polymers disclosed herein often aregreater than or equal to about 0.94 g/cm³, for example, greater than orequal to about 0.942 g/cm³, or greater than or equal to about 0.945g/cm³. Yet, in particular aspects, the density can be in a range fromabout 0.94 to about 0.96 g/cm³, from about 0.94 to about 0.955 g/cm³,from about 0.94 to about 0.95 g/cm³, from about 0.945 to about 0.96g/cm³, from about 0.942 to about 0.958 g/cm³, or from about 0.942 toabout 0.952 g/cm³.

While not being limited thereto, ethylene polymers described hereinoften can have a high load melt index (HLMI, I₂₁) in a range from about4 to about 20 g/10 min, from about 4 to about 18 g/10 min, or from about4 to about 16 g/10 min. In further aspects, ethylene polymers describedherein can have a HLMI in a range from about 5 to about 18 g/10 min,from about 5 to about 15 g/10 min, from about 5 to about 12 g/10 min,from about 6 to about 18 g/10 min, from about 6 to about 16 g/10 min, orfrom about 6 to about 14 g/10 min.

The ethylene polymers described herein have a very high zero-shearviscosity (η₀) at 190° C., which translates into excellent polymer meltstrength, and slump or sag resistance in pipe extrusion. In someaspects, the ethylene polymer can have a zero-shear viscosity (η₀) at190° C. in a range from about 20,000 to about 400,000 kPa-sec;alternatively, from about 30,000 to about 300,000 kPa-sec;alternatively, from about 30,000 to about 275,000 kPa-sec;alternatively, from about 35,000 to about 275,000 kPa-sec;alternatively, from about 20,000 to about 250,000 Pa-sec; alternatively,from about 25,000 to about 250,000 kPa-sec; alternatively, from about25,000 to about 230,000 kPa-sec; or alternatively, from about 30,000 toabout 215,000 kPa-sec. The zero-shear viscosity is determined fromviscosity data measured at 190° C. and using the Carreau-Yasuda (CY)empirical model as described herein, with creep adjustment.

Also indicative of the excellent polymer melt strength and slump or sagresistance in pipe extrusion, the disclosed ethylene polymers can have arelaxation time (τ_(η)) at 190° C. in a range from about 225 to about3000 sec. In some aspects, the relaxation time (τ_(η)) at 190° C. can bein a range from about 250 to about 2500 sec, or from about 275 to about2000 sec, while in other aspects, the relaxation time can range fromabout 300 to about 2500 sec, or from about 300 to about 2000 sec. Likezero-shear viscosity, the relaxation time (τ_(η)) at 190° C. isdetermined from viscosity data measured at 190° C. and using theCarreau-Yasuda (CY) empirical model as described herein, with creepadjustment.

Generally, ethylene polymers consistent with aspects of the presentinvention have levels of long chain branches (LCB) per 1000 total carbonatoms in a range from about 5 to about 50, from about 5 to about 35, orfrom about 5 to about 32 LCB per million total carbon atoms. In someaspects, the number of LCB per million total carbon atoms can be in arange from about 6 to about 28, from about 6 to about 26, or from about7 to about 20 LCB, per million total carbon atoms. The presence of LCBcan improve polymer melt strength and reduce or eliminate slump or sagin pipe extrusion.

Further, the ethylene polymers can be characterized by an average numberof LCB per Mw (vf) and, typically, this falls within a range from about0.15 to about 0.51. For example, the average number of LCB per Mw (vf)can be in range from about 0.16 to about 0.43, or from about 0.18 toabout 0.37.

Moreover, the ethylene polymers typically have a reverse short chainbranching distribution (reverse SCBD or reverse comonomer distribution,increasing comonomer distribution). A reverse SCBD can be characterizedby the number of short chain branches (SCB) per 1000 total carbon atomsof the ethylene polymer at Mw that is greater than at Mn, and/or thenumber of SCB per 1000 total carbon atoms of the ethylene polymer at Mzthat is greater than at Mn. The presence of more SCB at higher molecularweights can result in an ethylene polymer with improved toughness andstrength properties.

Further indicators of the excellent melt strength and slump or sagresistance of the disclosed ethylene polymers are the CY-a parameter,the viscosity at a shear rate of 0.01 sec⁻¹, and the viscosity at ashear rate of 0.001 sec⁻¹ (all measured at 190° C.). The CY-a parameterat 190° C. generally falls within a range from about 0.06 to about 0.25,such as from about 0.09 to about 0.2, from about 0.1 to about 0.18, fromabout 0.1 to about 0.16, or from about 0.12 to about 0.15. The viscosityat 0.01 sec⁻¹ {η (0.01)} of the polymer at 190° C. generally fallswithin a range from about 300 to about 800 kPa-sec, such as from about400 to about 700, from about 450 to about 750, from about 500 to about750, or from about 500 to about 650 kPa-sec. The viscosity at 0.001sec⁻¹ {η (0.001)} at 190° C. generally falls within a range from about800 to about 3000 kPa-sec, such as from about 900 to about 2800, fromabout 1000 to about 2600, from about 1000 to about 2300, from about 1200to about 2100, or from about 1300 to about 1900 kPa-sec. Theseviscosities and the CY-a parameter are determined from viscosity datameasured at 190° C. and using the Carreau-Yasuda (CY) empirical model asdescribed herein, with creep adjustment.

While not being limited thereto, the disclosed ethylene polymers oftencan have a 15 melt index (I₅) in a range from about 0.02 to about 0.3g/10 min, from about 0.02 to about 0.25 g/10 min, or from about 0.02 toabout 0.18 g/10 min. In further aspects, the ethylene polymer can have aI₅ in a range from about 0.03 to about 0.3 g/10 min, from about 0.03 toabout 0.25 g/10 min, from about 0.05 to about 0.3 g/10 min, from about0.05 to about 0.18 g/10 min, from about 0.06 to about 0.3 g/10 min, orfrom about 0.06 to about 0.15 g/10 min.

Ethylene polymers consistent with various aspects of the presentinvention generally have a broad molecular weight distribution, andoften with a weight-average molecular weight (Mw) in a range from about200,000 to about 500,000 g/mol, from about 220,000 to about 500,000g/mol, from about 210,000 to about 400,000 g/mol, from about 230,000 toabout 380,000 g/mol, or from about 250,000 to about 360,000 g/mol, andthe like. The ratio of Mw/Mn, or the polydispersity index, for theethylene polymers of this invention often can be greater than or equalto about 12 and less than or equal to about 40. Accordingly, suitableranges for the ratio of Mw/Mn can include from about 12 to about 40,from about 13 to about 38, from about 14 to about 39, from about 16 toabout 37, or from about 18 to about 35, and the like.

The ethylene polymers disclosed herein have excellent strength anddurability properties. In an aspect, the ethylene polymer can be furthercharacterized by a percent elongation at break (ASTM D638) that fallswithin a range from about 450 to about 850%, from about 500 to about800%, or from about 550 to about 750%. Additionally or alternatively,the ethylene polymer can be characterized by a yield strength (ASTMD638) ranging from about 3000 to about 5000 psi, from about 3500 toabout 4500 psi, or from about 3500 to about 4000 psi. Additionally oralternatively, the ethylene polymer can be characterized by an oxidativeinduction temperature (OIT, ASTM D3895) of at least about 200° C., atleast about 220° C., or at least about 240° C. Additionally oralternatively, the ethylene polymer can be characterized by a Charpyductile to brittle transition temperature (ASTM F2231) in a range fromabout −35 to about −5° C., or from about −30 to about −10° C.

Beneficially, the disclosed ethylene polymers can be capable ofproducing (or configured to produce) a pipe product having at least a24-inch diameter and at least a 2-inch wall thickness. For example, apipe product having a 78-inch diameter and a 3-inch wall thickness canbe produced without any slump or sag with the disclosed ethylenepolymers, and unexpectedly, this is not possible with high melt strengthchromium-catalyzed polymers. Further, despite the high molecular weightof the ethylene polymer, it has a relatively low gel content. Typically,this is quantified by less than 300 gels/ft², for gel sizes of at least200 microns, when extruded at a specific energy of less than 0.25kW-hr/kg. Given the high molecular weight of the ethylene polymer, thisgel level is unexpectedly low.

The ethylene polymer can be in any suitable form, such as fluff, powder,granulate, pellet, and the like. Often, the ethylene polymer is inpellet form. The ethylene polymer can contain one or more additives,non-limiting examples of which can include an antioxidant, an acidscavenger, an antiblock additive, a slip additive, a colorant, a filler,a processing aid, a UV inhibitor, and the like, as well as combinationsthereof. For instance, the colorant can be black (carbon black), white(titanium dioxide), or yellow for certain pipe applications. Thus, inaccordance with an aspect of this invention, the ethylene polymer canfurther comprise from about 0.5 to about 5 wt. %, from about 1 to about4 wt. %, or from about 2 to about 3 wt. %, of carbon black, although notlimited thereto. This weight percentage is based on the total weight ofthe ethylene polymer (inclusive of all additives).

Often, the ethylene polymer can contain an acid scavenger, such as zincstearate, calcium stearate, hydrotalcite, and the like, or combinationsthereof. Typical loadings, based on the total weight of the ethylenepolymer, include from about 100 ppm to about 1000 ppm, from about 250ppm to about 800 ppm, or from about 350 ppm to about 750 ppm, of acidscavenger. Additionally or alternatively, the ethylene polymer cancontain a processing aid, such as a fluoroelastomer or a fluoropolymer;combinations of two or more processing aids can be used. Typicalloadings, based on the total weight of the ethylene polymer, includefrom about 100 ppm to about 1000 ppm, from about 250 ppm to about 750ppm, or from about 300 ppm to about 600 ppm, of processing aid.

Additionally or alternatively, the ethylene polymer can contain aphenolic antioxidant, such as IRGANOX 1010 (pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), IRGANOX 1076(octadecyl-3-(3,5-di-tertbutyl-4-hydroxyphenyl) propionate), IRGANOX1330(1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene),and the like, or any combination thereof. Typical loadings, based on thetotal weight of the ethylene polymer, include from about 250 ppm toabout 5000 ppm; alternatively, from about 500 ppm to about 5000 ppm;alternatively, from about 1000 ppm to about 4500 ppm; alternatively,from about 1500 ppm to about 4000 ppm; or alternatively, from about 2000ppm to about 3500 ppm, of phenolic antioxidant.

Additionally or alternatively, the ethylene polymer can contain aphosphite antioxidant, such as IRGAFOS 168(tris(2,4,6-di-tert-butylphenyl) phosphite), ULTRANOX 627A(bis(2,4-di-t-butylphenyl) pentraerythritol diphosphite plusstabilizer), ULTRANOX 626 (bis(2,4-di-t-butylphenyl) pentraerythritoldiphosphite), PEP-36 (bis (2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphate), DOVERPHOS 9228T (bis(2,4-dicumylphenyl)pentaerythritol diphosphite), and the like, or any combination thereof.Typical loadings, based on the total weight of the ethylene polymer,include from about 250 ppm to about 5000 ppm; alternatively, from about250 ppm to about 4000 ppm; alternatively, from about 250 ppm to about3000 ppm; alternatively, from about 500 ppm to about 5000 ppm;alternatively, from about 500 ppm to about 3500 ppm; alternatively, fromabout 500 ppm to about 2500 ppm; alternatively, from about 700 ppm toabout 5000 ppm; alternatively, from about 700 ppm to about 4000 ppm;alternatively, from about 700 ppm to about 2500 ppm; alternatively, fromabout 1000 ppm to about 5000 ppm; or alternatively, from about 1000 ppmto about 3500 ppm, of phosphite antioxidant.

Generally, the total amount of antioxidant(s) present in the ethylenepolymer is less than or equal to about 5000 ppm, although this is not arequirement. Thus, in some aspects, the total phenolic and phosphiteantioxidant loading in the ethylene polymer can be less than or equal toabout 5000 ppm, 4500 ppm, or 4000 ppm.

Optionally, the ethylene polymer can further contain one or moresuitable UV inhibitors (inclusive of UV absorbers and hindered aminelight stabilizers (HALS)). When present, the total UV inhibitor contentoften can range from about 250 ppm to about 7500 ppm; alternatively,from about 250 ppm to about 6500 ppm; alternatively, from about 250 ppmto about 5000 ppm; alternatively, from about 500 ppm to about 6000 ppm;alternatively, from about 500 ppm to about 4000 ppm; or alternatively,from about 1000 ppm to about 5000 ppm, of UV inhibitor.

Consistent with aspects of the present invention, the ethylene polymercan be produced from a base resin (discussed herein below) via a processcomprising contacting the base resin with a peroxide compound to producethe ethylene polymer (any ethylene polymer disclosed herein). Generally,the amount (ppm by weight) of the peroxide compound used in the processis of lesser interest, because the amount of peroxide groups is moreimportant, and the molecular weight and the number of peroxide groupsper peroxide compound are not consistent amongst all suitable peroxidecompounds. Generally, the amount of peroxide groups, based on the weightof the base resin, can be in a range from about 60 to about 200 ppm,from about 75 to about 175 ppm, or from about 100 to about 150 ppm, ofperoxide groups, based on the weight of the base resin.

The base resin and the peroxide compound, therefore, can be contacted ata temperature sufficient to generate peroxide groups at about 60 toabout 200 ppm, from about 75 to about 175 ppm, or from about 100 toabout 150 ppm, of peroxide groups, based on the weight of the baseresin.

In an aspect, the step of contacting the base resin with the peroxidecompound can comprise melt processing a blend (or mixture) of the baseresin and the peroxide compound at any suitable melt processingtemperature, such as, for example, a temperature in a range from about120 to about 300° C., a temperature in a range from about 150 to about250° C., a temperature in a range from about 175 to about 225° C., andso forth. The appropriate temperature may depend upon the composition ofthe peroxide compound and the temperature at which it liberates peroxidegroups. Prior to contacting the peroxide compound, the base resin can bein any suitable form including, for example, fluff, powder, granulate,pellet, solution, slurry, emulsion, and the like. Similarly, theperoxide compound can be in solid form, in liquid form, in a solution,or in a slurry. One particular method uses a masterbatch of the peroxidecompound, and contacts the base resin (in fluff form) during meltprocessing. The masterbatch of the peroxide compound can contain anysuitable organic or inorganic carrier, but often contains a high meltflow carrier resin, such as a polyethylene or polypropylene.

The present invention is not limited to any particular method ofcontacting and melt processing the base resin and the peroxide compound.Various methods of mixing and/or compounding can be employed, as wouldbe recognized by those of skill in the art. In one aspect, the meltprocessing of the base resin and the peroxide compound can be performedin a single screw extrusion system. In another aspect, the meltprocessing of the base resin and the peroxide compound can be performedin a twin screw extrusion system (e.g., a counter-rotating mixer or aco-rotating twin screw extrusion system). The twin screw extrusionsystem can include any combination of feeding, melting, mixing, andconveying elements. For instance, the twin screw extrusion system cancontain all or a majority of mixing elements.

The peroxide compound can be any compound containing one or moreperoxide (O—O) groups, suitable examples of which can include, but arenot limited to, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumylperoxide, t-butyl cumyl peroxide,n-butyl-4,4′-di(t-butylperoxy)valerate, and the like. The peroxidecompound can be, for instance, added as a solid prill, dissolved in amineral oil, or in a liquid form.

One or more additives also can be added during the conversion of thebase resin (and peroxide compound) to the ethylene polymer. Non-limitingexamples of suitable additives can include an antioxidant, an acidscavenger, an antiblock additive, a slip additive, a colorant, a filler,a processing aid, a UV inhibitor, and the like. Combinations of two ormore additives can be contacted with the base resin and the peroxidecompound, if desired.

Articles and Pipe Products

Articles of manufacture can be formed from, and/or can comprise, any ofthe ethylene polymers of this invention and, accordingly, areencompassed herein. For example, articles which can comprise ethylenepolymers of this invention can include, but are not limited to, anagricultural film, an automobile part, a bottle, a container forchemicals, a drum, a fiber or fabric, a food packaging film orcontainer, a food service article, a fuel tank, a geomembrane, ahousehold container, a liner, a molded product, a medical device ormaterial, an outdoor storage product, outdoor play equipment, a pipe, asheet or tape, a toy, or a traffic barrier, and the like. Variousprocesses can be employed to form these articles. Non-limiting examplesof these processes include injection molding, blow molding, rotationalmolding, film extrusion, sheet extrusion, profile extrusion,thermoforming, and the like. Additionally, additives and modifiers oftenare added to these polymers in order to provide beneficial polymerprocessing or end-use product attributes. Such processes and materialsare described in Modern Plastics Encyclopedia, Mid-November 1995 Issue,Vol. 72, No. 12; and Film Extrusion Manual—Process, Materials,Properties, TAPPI Press, 1992; the disclosures of which are incorporatedherein by reference in their entirety. In some aspects of thisinvention, an article of manufacture can comprise any of ethylenepolymers described herein, and the article of manufacture can be or cancomprise a large diameter pipe.

In some aspects, the article produced from and/or comprising any of theethylene polymers disclosed herein is a pipe product. For instance, thepipe can be characterized by any of the properties of the ethylenepolymers disclosed herein. Thus, the pipe can be characterized by (e.g.,a sample of the pipe product can be analyzed and determined to have) adensity of at least about 0.94 g/cm³, a HLMI (I₂₁) in a range from about4 to about 20 g/10 min, a zero-shear viscosity (η₀) at 190° C. in arange from about 20,000 to about 400,000 kPa-sec, and a relaxation time(τ_(η)) at 190° C. in a range from about 225 to about 3000 sec.

The pipe also can contain one or more additives, non-limiting examplesof which can include an antioxidant, an acid scavenger, an antiblockadditive, a slip additive, a colorant, a filler, a processing aid, a UVinhibitor, and the like. Combinations of two or more additives can bepresent in the pipe product. As would be recognized by those of skill inthe art, certain additives can increase the density of the ethylenepolymer or the pipe product, such as antiblock additives and colorants(e.g., carbon black). Thus, a black ethylene polymer (or a black pipeproduct) can have a density that is 0.01-0.04 g/cm³, or more, greaterthan that of a natural ethylene polymer (or a natural pipe product),which does not contain an antiblock and/or a colorant. Accordingly, thedensity of colored ethylene polymers (or colored pipe products) canrange from about 0.94 g/cm³ to about 1.05 g/cm³, from about 0.945 toabout 1.04 g/cm³, from about 0.95 to about 1.04 g/cm³, or from about0.95 to about 1.02 g/cm³.

The wall thickness of the pipe product is not particularly limited, andcan range from about 0.1 to about 5 inches, from about 0.5 to about 5inches, from about 1 to about 4 inches, or from about 2 to about 3inches. However, the ethylene polymers disclosed herein are well suitedfor the production of thick-wall pipe, which depending upon the end-useapplication, can have wall thicknesses of at least about 2 inches, andoften can range up to 3 to 5 inches.

Likewise, the diameter (outside diameter) of the pipe is not limited toany particular range. Pipe products having outer pipe diameters of fromabout ¼ to about 100 inches, from about 3 to about 12 inches, from about12 to about 100 inches, or from about 24 to about 63 inches, areencompassed herein. As above, the ethylene polymers disclosed herein arewell suited for the production of large diameter pipe, which dependingupon the end-use application, can have outer diameters of at least about24 inches, and often can range up to 36-100 inches, or 36-60 inches.

In one aspect of this invention, the pipe can have a hydrostaticstrength of 1600 psi at 23° C. for 100,000 hr, while in another aspect,the pipe can have a hydrostatic strength of 1000 psi at 60° C. for100,000 hr, and in yet another aspect, the pipe can have both ahydrostatic strength of 1600 psi at 23° C. for 100,000 hr and ahydrostatic strength of 1000 psi at 60° C. for 100,000 hr. Theseparameters are measured in accordance with ASTM D1598 and ASTM D2837.

The pipe products disclosed herein have excellent performance inchlorinated water environments. As an example, the pipe can have afailure time of at least 1200 hr under chlorinated water conditions at90° C. and 450 psi (ASTM F2263-07e1). In further aspects, the pipe canhave a failure time of at least 3400 hr, or at least 7400 hr, underchlorinated water conditions at 90° C. and 450 psi (ASTM F2263-07e1).The pipe can have a failure time that may range as high as 8000-9500hours, but the test is typically stopped after a specified number ofhours is reached (e.g., 1200 hr or 3400 hr or 7400 hr), and given thelong duration of test, the upper limit (in hours) is generally notdetermined.

As disclosed herein, the pipe product can contain any combination ofadditives suitable for the end-use application of the pipe. For example,a black pipe product can contain from about 0.5 to about 5 wt. %, fromabout 1 to about 4 wt. %, or from about 2 to about 3 wt. %, or carbonblack, based on the total weight of the pipe. In addition to colorants,other suitable pipe additives include antioxidants, acid scavengers,antiblock additives, slip additives, fillers, processing aids, UVinhibitors, and the like, as well as combinations thereof. Similar tothe ethylene polymers described hereinabove, the pipe often can containone of more of an acid scavenger, processing aid, phenolic antioxidant,and phosphite antioxidant. Selections for these additives and typicaladdition amounts can be the same as those described above in relation tothe ethylene polymer.

Also contemplated herein is a method for making or forming a pipecomprising any ethylene polymer disclosed herein. One such method cancomprise melt processing the ethylene polymer through a pipe die to formthe pipe. Moreover, any suitable means of melt processing can beemployed, although extrusion typically can be utilized. As above, one ormore additives can be combined with the ethylene polymer in the meltprocessing step (extrusion step), such as antioxidants, acid scavengers,antiblock additives, slip additives, colorants, fillers, processingaids, UV inhibitors, and the like, as well as combinations thereof.Thus, the method of making a pipe can comprise melt processing theethylene polymer and at least one additive through the pipe die to formthe pipe.

Pipes formed by these methods also are encompassed herein, and the pipesformed by these methods can have any of the properties orcharacteristics of the ethylene polymer and/or pipe product disclosedherein.

Base Resins

Generally, the base resin used to produce the ethylene polymer can beany homopolymer of ethylene or copolymer, terpolymer, etc., of ethyleneand at least one olefin comonomer disclosed hereinabove for the ethylenepolymer. Thus, the base resin can comprise an ethylene/α-olefincopolymer, while in another aspect, the base resin can comprise anethylene homopolymer, and in yet another aspect, the base resin cancomprise an ethylene/α-olefin copolymer and an ethylene homopolymer.Accordingly, the base resin can comprise an ethylene/1-butene copolymer,an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, anethylene homopolymer, or any combination thereof alternatively, anethylene/1-butene copolymer, an ethylene/1-hexene copolymer, anethylene/1-octene copolymer, or any combination thereof; oralternatively, an ethylene/1-hexene copolymer. Typically, for example,if the base resin is an ethylene/1-hexene copolymer, then the ethylenepolymer produced from the base resin also is an ethylene/1-hexenecopolymer, although mixtures and combinations of various types ofhomopolymers and copolymers can be used.

In order to produce an ethylene polymer having the properties andbenefits disclosed herein, a suitable base resin is used. Anillustrative and non-limiting example of a base resin (e.g., comprisingan ethylene copolymer) of the present invention can have a density of atleast about 0.94 g/cm³, a HLMI (I₂₁) in a range from about 4 to about 25g/10 min, a Mw in a range from about 200,000 to about 500,000 g/mol, anda ratio of Mw/Mn in a range from about 12 to about 40. Anotherillustrative and non-limiting example of a base resin (e.g., comprisingan ethylene copolymer) of the present invention can have a density in arange from about 0.94 to about 0.96, a HLMI (I₂₁) in a range from about6 to about 18 g/10 min, a Mw in a range from about 210,000 to about400,000 g/mol, and a ratio of Mw/Mn in a range from about 18 to about35. These illustrative and non-limiting examples of base resinsconsistent with the present invention also can have any of the polymerproperties listed below and in any combination, unless indicatedotherwise.

The densities of the base resin used to produce ethylene polymersdisclosed herein often are greater than or equal to about 0.94 g/cm³,for example, greater than or equal to about 0.942 g/cm³, or greater thanor equal to about 0.945 g/cm³. Yet, in particular aspects, the densitycan be in a range from about 0.94 to about 0.96 g/cm³, from about 0.94to about 0.955 g/cm³, from about 0.94 to about 0.95 g/cm³, from about0.945 to about 0.96 g/cm³, from about 0.942 to about 0.958 g/cm³, orfrom about 0.942 to about 0.952 g/cm³.

The base resin used to produce ethylene polymers in accordance with someaspects of this invention generally can have a high load melt index(HLMI, I₂₁) in a range from about 4 to about 25 g/10 min. For example,the base resin can have a HLMI in a range from about 5 to about 25, fromabout 5 to about 20, from about 6 to about 20, from about 7 to about 25,from about 7 to about 18, from about 8 to about 16, or from about 9 toabout 15 g/10 min.

Additionally, the base resin can have a ratio of HLMI/I₅ of greater thanabout 15 and less than about 50. Suitable ranges for HLMI/I₅ caninclude, but are not limited to, from about 15 to about 45, from about20 to about 50, from about 20 to about 45, from about 25 to about 45,from about 25 to about 40, or from about 29 to about 35, and the like.

Base resins consistent with various aspects of the present inventiongenerally have a broad molecular weight distribution, and often with aweight-average molecular weight (Mw) in a range from about 200,000 toabout 500,000 g/mol, from about 220,000 to about 500,000 g/mol, fromabout 210,000 to about 400,000 g/mol, from about 230,000 to about380,000 g/mol, or from about 250,000 to about 360,000 g/mol, and thelike. Likewise, suitable non-limiting ranges of the number-averagemolecular weight (Mn) can include from about 8,000 to about 20,000g/mol, from about 9,000 to about 18,000 g/mol, or from about 10,000 toabout 16,000 g/mol, and the like. Further, suitable ranges for thez-average molecular weight (Mz) can include, for instance, from about1,000,000 to about 2,500,000, from about 1,000,000 to about 2,300,000,or from about 1,100,000 to about 2,200,000 g/mol, and the like.

The ratio of Mw/Mn, or the polydispersity index, for the base resins ofthis invention often can be greater than or equal to about 12 and lessthan or equal to about 40. Accordingly, suitable ranges for the ratio ofMw/Mn can include from about 12 to about 40, from about 13 to about 38,from about 14 to about 39, from about 16 to about 37, or from about 18to about 35, and the like.

Base resins described herein can, in some aspects, have a reversecomonomer distribution, i.e., a short chain branch content thatgenerally increases as molecular weight increases, for example, thehigher molecular weight components of the polymer generally have highercomonomer incorporation than the lower molecular weight components.Typically, there is increasing comonomer incorporation with increasingmolecular weight. For instance, the number of short chain branches (SCB)per 1000 total carbon atoms can be greater at Mw than at Mn.Additionally or alternatively, the number of short chain branches (SCB)per 1000 total carbon atoms can be greater at Mz than at Mn.

Consistent with aspects of this invention, the base resin (e.g., anethylene/α-olefin copolymer) can comprise a high or higher molecularweight (HMW) component (or a first component) and a low or lowermolecular weight (LMW) component (or a second component). Thesecomponent terms are relative, are used in reference to each other, andare not limited to the actual molecular weights of the respectivecomponents. The molecular weight characteristics of these LMW and HMWcomponents can be determined by deconvoluting the composite (overallpolymer) molecular weight distribution (e.g., determined using gelpermeation chromatography). The amount of the higher molecular weightcomponent, based on the total polymer (the base resin), is not limitedto any particular range. Generally, however, the amount of the highermolecular weight component can be in a range from about 35 to about 65wt. %, from about 40 to about 60 wt. %, or from about 45 to about 55 wt.%.

The density of the higher molecular weight component of the base resinoften is less than or equal to about 0.94 g/cm³. For example, the highermolecular weight component can have a density in a range from about0.915 to about 0.94, from about 0.92 to about 0.94, from about 0.92 toabout 0.93, or from about 0.922 to about 0.932 g/cm³.

The melt flow rate of the higher molecular weight component of the baseresin can be quantified with a high load melt index: HLMI₂₇₅ (I₂₁ usinga 2.75 mm diameter capillary). The HLMI₂₇₅ (I₂₁ using a 2.75 mm diametercapillary) of the higher molecular weight component generally rangesfrom about 0.2 to about 1, from about 0.3 to about 0.9, or from about0.4 to about 0.8 g/10 min.

The molecular weight distribution of the higher molecular weightcomponent of the base resin generally can be characterized as follows.The ratio of Mw/Mn of the higher molecular weight component can rangefrom about 4 to about 8, from about 4 to about 7, from about 4.5 toabout 6.5, or from about 5 to about 6. Suitable non-limiting ranges ofthe number-average molecular weight (Mn) for the higher molecular weightcomponent can include from about 80,000 to about 120,000, or from about90,000 to about 110,000 g/mol. Likewise, suitable non-limiting ranges ofthe weight-average molecular weight (Mw) for the higher molecular weightcomponent can include from about 425,000 to about 650,000, or from about500,000 to about 600,000 g/mol. Additionally, suitable non-limitingranges of the z-average molecular weight (Mz) for the higher molecularweight component can include from about 1,500,000 to about 2,500,000, orfrom about 1,600,000 to about 2,000,000 g/mol.

The molecular weight distribution of the lower molecular weightcomponent of the base resin generally can be characterized as follows.The ratio of Mw/Mn of the lower molecular weight component can rangefrom about 4 to about 8, from about 4 to about 7, from about 4.5 toabout 6.5, or from about 4.5 to about 6. Suitable non-limiting ranges ofthe Mn for the lower molecular weight component can include from about4,000 to about 8,000, or from about 5,000 to about 7,000 g/mol.Likewise, suitable non-limiting ranges of the Mw for the lower molecularweight component can include from about 20,000 to about 40,000, or fromabout 25,000 to about 35,000 g/mol. Additionally, suitable non-limitingranges of the Mz for the lower molecular weight component can includefrom about 50,000 to about 110,000, or from about 65,000 to about 95,000g/mol.

Although one or more additives can be incorporated during the conversionof the base resin to the ethylene polymer, or during the conversion ofthe ethylene polymer to the pipe product (or to other article ofmanufacture), the base resin also can contain one or more suitableadditives. Non-limiting examples of suitable additives can include anantioxidant, an acid scavenger, an antiblock additive, a slip additive,a colorant, a filler, a processing aid, a UV inhibitor, and the like.Combinations of two or more additives can be present in the base resin.Selections for these additives and typical addition amounts can be thesame as those described above in relation to the ethylene polymer.

Consistent with aspects of the present invention, the base resin can beproduced using a Ziegler-Natta catalyst system, and the catalyst systemcan be heterogeneous or homogeneous. The catalyst can have a titaniumcontent in the 2-12 wt. % range, the 4-12 wt. % range, or the 6-10 wt. %range, and can contain titanium trichloride, titanium tetrachloride,magnesium chloride, or any combination thereof. In some aspects, thecatalyst is a solid catalyst. Any suitable co-catalyst can be used, suchas an alkyl aluminum co-catalyst.

Base resins can be produced from the disclosed catalyst systems usingany suitable olefin polymerization process using various types ofpolymerization reactors, polymerization reactor systems, andpolymerization reaction conditions. One such olefin polymerizationprocess for polymerizing olefins in the presence of a catalystcomposition of the present invention can comprise contacting thecatalyst composition with an ethylene and optionally an olefin comonomer(one or more) in a polymerization reactor system under polymerizationconditions to produce the base resin.

As used herein, a “polymerization reactor” includes any polymerizationreactor capable of polymerizing olefin monomers and comonomers (one ormore than one comonomer) to produce homopolymers, copolymers,terpolymers, and the like. The various types of polymerization reactorsinclude those that can be referred to as a batch reactor, slurryreactor, gas-phase reactor, solution reactor, high pressure reactor,tubular reactor, autoclave reactor, and the like, or combinationsthereof; or alternatively, the polymerization reactor system cancomprise a slurry reactor, a gas-phase reactor, a solution reactor, or acombination thereof. The polymerization conditions for the variousreactor types are well known to those of skill in the art. Gas phasereactors can comprise fluidized bed reactors or staged horizontalreactors. Slurry reactors can comprise vertical or horizontal loops.High pressure reactors can comprise autoclave or tubular reactors.Reactor types can include batch or continuous processes. Continuousprocesses can use intermittent or continuous product discharge.Polymerization reactor systems and processes also can include partial orfull direct recycle of unreacted monomer, unreacted comonomer, and/ordiluent.

A polymerization reactor system can comprise a single reactor ormultiple reactors (2 reactors, more than 2 reactors, etc.) of the sameor different type. For instance, the polymerization reactor system cancomprise a slurry reactor, a gas-phase reactor, a solution reactor, or acombination of two or more of these reactors. Production of polymers inmultiple reactors can include several stages in at least two separatepolymerization reactors interconnected by a transfer device making itpossible to transfer the polymers resulting from the firstpolymerization reactor into the second reactor. The desiredpolymerization conditions in one of the reactors can be different fromthe operating conditions of the other reactor(s). Alternatively,polymerization in multiple reactors can include the manual transfer ofpolymer from one reactor to subsequent reactors for continuedpolymerization. Multiple reactor systems can include any combinationincluding, but not limited to, multiple loop reactors, multiple gasphase reactors, a combination of loop and gas phase reactors, multiplehigh pressure reactors, or a combination of high pressure with loopand/or gas phase reactors. The multiple reactors can be operated inseries, in parallel, or both. Accordingly, the present inventionencompasses polymerization reactor systems comprising a single reactor,comprising two reactors, and comprising more than two reactors. Thepolymerization reactor system can comprise a slurry reactor, a gas-phasereactor, a solution reactor, in certain aspects of this invention, aswell as multi-reactor combinations thereof.

According to one aspect, the polymerization reactor system can compriseat least one loop slurry reactor comprising vertical or horizontalloops. Monomer, diluent, catalyst, and comonomer can be continuously fedto a loop reactor where polymerization occurs. Generally, continuousprocesses can comprise the continuous introduction of monomer/comonomer,a catalyst, and a diluent into a polymerization reactor and thecontinuous removal from this reactor of a suspension comprising polymerparticles and the diluent. Reactor effluent can be flashed to remove thesolid polymer from the liquids that comprise the diluent, monomer and/orcomonomer. Various technologies can be used for this separation stepincluding, but not limited to, flashing that can include any combinationof heat addition and pressure reduction, separation by cyclonic actionin either a cyclone or hydrocyclone, or separation by centrifugation.

In an aspect of this invention, the base resin can be produced in a dualloop slurry reactor. For instance, the base resin can be produced in twoloop reactors operating in series, using a Ziegler-Natta catalyst.Often, comonomer can be fed to the first reactor, and the high molecularweight component of the base resin can be produced in the first reactor,and the low molecular weight component of the base resin can be producedin the second reactor.

A typical slurry polymerization process (also known as the particle formprocess) is disclosed, for example, in U.S. Pat. Nos. 3,248,179,4,501,885, 5,565,175, 5,575,979, 6,239,235, 6,262,191, 6,833,415, and8,822,608, each of which is incorporated herein by reference in itsentirety.

Suitable diluents used in slurry polymerization include, but are notlimited to, the monomer being polymerized and hydrocarbons that areliquids under reaction conditions. Examples of suitable diluentsinclude, but are not limited to, hydrocarbons such as propane,cyclohexane, isobutane, n-butane, n-pentane, isopentane, neopentane, andn-hexane. Some loop polymerization reactions can occur under bulkconditions where no diluent is used.

According to yet another aspect, the polymerization reactor system cancomprise at least one gas phase reactor (e.g., a fluidized bed reactor).Such reactor systems can employ a continuous recycle stream containingone or more monomers continuously cycled through a fluidized bed in thepresence of the catalyst under polymerization conditions. A recyclestream can be withdrawn from the fluidized bed and recycled back intothe reactor. Simultaneously, polymer product can be withdrawn from thereactor and new or fresh monomer can be added to replace the polymerizedmonomer. Such gas phase reactors can comprise a process for multi-stepgas-phase polymerization of olefins, in which olefins are polymerized inthe gaseous phase in at least two independent gas-phase polymerizationzones while feeding a catalyst-containing polymer formed in a firstpolymerization zone to a second polymerization zone. Representative gasphase reactors are disclosed in U.S. Pat. Nos. 5,352,749, 4,588,790,5,436,304, 7,531,606, and 7,598,327, each of which is incorporated byreference in its entirety herein.

According to still another aspect, the polymerization reactor system cancomprise a high pressure polymerization reactor, e.g., can comprise atubular reactor or an autoclave reactor. Tubular reactors can haveseveral zones where fresh monomer, initiators, or catalysts are added.Monomer can be entrained in an inert gaseous stream and introduced atone zone of the reactor. Initiators, catalysts, and/or catalystcomponents can be entrained in a gaseous stream and introduced atanother zone of the reactor. The gas streams can be intermixed forpolymerization. Heat and pressure can be employed appropriately toobtain optimal polymerization reaction conditions.

According to yet another aspect, the polymerization reactor system cancomprise a solution polymerization reactor wherein the monomer/comonomerare contacted with the catalyst composition by suitable stirring orother means. A carrier comprising an inert organic diluent or excessmonomer can be employed. If desired, the monomer/comonomer can bebrought in the vapor phase into contact with the catalytic reactionproduct, in the presence or absence of liquid material. Thepolymerization zone can be maintained at temperatures and pressures thatwill result in the formation of a solution of the polymer in a reactionmedium. Agitation can be employed to obtain better temperature controland to maintain uniform polymerization mixtures throughout thepolymerization zone. Adequate means are utilized for dissipating theexothermic heat of polymerization.

The polymerization reactor system can further comprise any combinationof at least one raw material feed system, at least one feed system forcatalyst or catalyst components, and/or at least one polymer recoverysystem. Suitable reactor systems can further comprise systems forfeedstock purification, catalyst storage and preparation, extrusion,reactor cooling, polymer recovery, fractionation, recycle, storage,loadout, laboratory analysis, and process control. Depending upon thedesired properties of the olefin polymer, hydrogen can be added to thepolymerization reactor as needed (e.g., continuously, pulsed, etc.).

Polymerization conditions that can be controlled for efficiency and toprovide desired polymer properties can include temperature, pressure,and the concentrations of various reactants. Polymerization temperaturecan affect catalyst productivity, polymer molecular weight, andmolecular weight distribution. Various polymerization conditions can beheld substantially constant, for example, for the production of aparticular grade of the olefin polymer (or ethylene polymer). A suitablepolymerization temperature can be any temperature below thede-polymerization temperature according to the Gibbs Free energyequation. Typically, this includes from about 60° C. to about 280° C.,for example, or from about 60° C. to about 120° C., depending upon thetype of polymerization reactor(s). In some reactor systems, thepolymerization temperature generally can be within a range from about70° C. to about 100° C., or from about 75° C. to about 95° C.

Suitable pressures will also vary according to the reactor andpolymerization type. The pressure for liquid phase polymerizations in aloop reactor is typically less than 1000 psig (6.9 MPa). Pressure forgas phase polymerization is usually at about 200 to 500 psig (1.4 MPa to3.4 MPa). High pressure polymerization in tubular or autoclave reactorsis generally run at about 20,000 to 75,000 psig (138 to 517 MPa).Polymerization reactors can also be operated in a supercritical regionoccurring at generally higher temperatures and pressures. Operationabove the critical point of a pressure/temperature diagram(supercritical phase) can offer advantages to the polymerizationreaction process.

Consistent with aspects of this invention, the olefin monomer used inthe polymerization process can comprise ethylene, and the comonomer cancomprise a C₃-C₁₀ alpha-olefin; alternatively, the comonomer cancomprise 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, styrene, orany combination thereof; alternatively, the comonomer can comprise1-butene, 1-hexene, 1-octene, or any combination thereof; alternatively,the comonomer can comprise 1-butene; alternatively, the comonomer cancomprise 1-hexene; or alternatively, the comonomer can comprise1-octene.

Examples

The invention is further illustrated by the following examples, whichare not to be construed in any way as imposing limitations to the scopeof this invention. Various other aspects, embodiments, modifications,and equivalents thereof which, after reading the description herein, maysuggest themselves to one of ordinary skill in the art without departingfrom the spirit of the present invention or the scope of the appendedclaims.

The high load melt index (HLMI, I₂₁, g/10 min) was determined inaccordance with ASTM D1238 at 190° C. with a 21.6 kg weight, and the 15melt index (g/10 min) was determined in accordance with ASTM D1238 at190° C. with a 5 kg weight. HLMI₂₇₅ (I₂₁ using a 2.75 mm diametercapillary) was determined in accordance with ASTM D1238 at 190° C. witha 21.6 kg weight, but using a 2.75 mm diameter capillary. Density wasdetermined in grams per cubic centimeter (g/cm³) on a compression moldedsample, cooled at 15° C. per hour, and conditioned for 40 hours at roomtemperature in accordance with ASTM D1505 and ASTM D4703.

Molecular weights and molecular weight distributions were obtained usinga PL-GPC 220 (Polymer Labs, an Agilent Company) system equipped with aIR4 detector (Polymer Char, Spain) and three Styragel HMW-6E GPC columns(Waters, Mass.) running at 145° C. The flow rate of the mobile phase1,2,4-trichlorobenzene (TCB) containing 0.5 g/L2,6-di-t-butyl-4-methylphenol (BHT) was set at 1 mL/min, and polymersolution concentrations were in the range of 1.0-1.5 mg/mL, depending onthe molecular weight. Sample preparation was conducted at 150° C. fornominally 4 hr with occasional and gentle agitation, before thesolutions were transferred to sample vials for injection. An injectionvolume of about 200 μL was used. The integral calibration method wasused to deduce molecular weights and molecular weight distributionsusing a broad Chevron Phillips Chemical Company's HDPE polyethyleneresin, MARLEX BHB5003, as the standard. The integral table of thestandard was predetermined in a separate experiment with SEC-MALS. Mn isthe number-average molecular weight, Mw is the weight-average molecularweight, and Mz is the z-average molecular weight.

Melt rheological characterizations were performed as follows.Small-strain (10%) oscillatory shear measurements were performed on anAnton Paar MCR 501 rheometer using parallel-plate geometry. Allrheological tests were performed at 190° C. The complex viscosity |η*|versus frequency (ω) data were then curve fitted using the modifiedthree parameter Carreau-Yasuda (CY) empirical model to obtain the zeroshear viscosity—η₀, characteristic viscous relaxation time—τ_(η), andthe breadth parameter—a (CY-a parameter). The simplified Carreau-Yasuda(CY) empirical model is as follows.

${{{\eta^{*}(\omega)}} = \frac{\eta_{0}}{\left\lbrack {1 + \left( {\tau_{\eta}\omega} \right)^{a}} \right\rbrack^{{({1 - n})}/a}}},$

wherein:

-   -   |η*(ω)|=magnitude of complex shear viscosity;    -   η₀=zero shear viscosity;    -   τ_(η)=viscous relaxation time (Tau(η) in sec);    -   a=“breadth” parameter (CY-a parameter);    -   n=fixes the final power law slope, fixed at 2/11; and    -   ω=angular frequency of oscillatory shearing deformation.

Details of the significance and interpretation of the CY model andderived parameters can be found in: C. A. Hieber and H. H. Chiang,Rheol. Acta, 28, 321 (1989); C. A. Hieber and H. H. Chiang, Polym. Eng.Sci., 32, 931 (1992); and R. B. Bird, R. C. Armstrong and O. Hasseger,Dynamics of Polymeric Liquids, Volume 1, Fluid Mechanics, 2nd Edition,John Wiley & Sons (1987); each of which is incorporated herein byreference in its entirety.

A creep adjustment was used to extend the low frequency range ofrheological characterization to 10⁻⁴ sec⁻¹. In the creep test, aconstant shear stress σ₀ was applied to the specimen and the shearstrain γ was recorded as a function of creep time t. Although thetime-dependent data generated by the creep and creep recovery tests lookdifferent from the frequency-dependent data measured in the dynamicfrequency sweep test, as long as the measurements are performed in thelinear viscoelastic regime, these two experimental data sets contain thesame rheological information, so that the time-dependent creepcompliance data can be transformed into the frequency-dependent dynamicdata, and thus the long time creep measurement can supplement the lowfrequency data of the dynamic frequency sweep measurement. Details ofthe test method and analysis can be found in Y. W. Inn and D. C.Rohlfing, “Application of creep test to obtain the linear viscoelasticproperties at low frequency range for polyethylene melts” AppliedRheology 22 (2012), incorporated herein by reference in its entirety.

The generalized Voigt model was used for modeling the time-dependentcreep compliance J(t)=γ(t)/σ₀ in terms of a discrete spectrum J_(k) ofretardation times τ_(k) and zero shear rate viscosity η₀,

${J(t)} = {{\sum\limits_{k = 1}^{N}\; {J_{k}\left( {1 - e^{{- t}/\tau_{k}}} \right)}} + {\frac{t}{\eta_{0}}.}}$

If the discrete retardation spectrum accurately describes the compliancedata, the theory of linear viscoelasticity permits a quantitativedescription of other types of experimental data, for example, thestorage and the loss compliance calculated as

${{J^{\prime}(\omega)} = {\sum\limits_{k = 1}^{N}{J_{k}\frac{1}{1 + {\omega^{2}\tau_{k}^{2}}}}}},{{J^{''}(\omega)} = {\frac{1}{\omega \; \eta_{0}} + {\sum\limits_{k = 1}^{N}{J_{k}{\frac{\omega \; \tau_{k}}{1 + {\omega^{2}\tau_{k}^{2}}}.}}}}}$

From the relationship between the complex modulus and the complexcompliance, the storage and loss modulus of dynamic frequency sweep datacan be obtained as

${{G^{\prime}(\omega)} = \frac{J^{\prime}(\omega)}{\left\lbrack {J^{\prime}(\omega)} \right\rbrack^{2} + \left\lbrack {J^{''}(\omega)} \right\rbrack^{2}}},{{G^{\prime}(\omega)} = {\frac{J^{''}(\omega)}{\left\lbrack {J^{\prime}(\omega)} \right\rbrack^{2} + \left\lbrack {J^{''}(\omega)} \right\rbrack^{2}}.}}$

As a simple numerical approach to obtain the discrete spectrum ofretardation times, the Microsoft Excel Solver tool can be used byminimizing the following objective function O.

$O = {\sum\limits_{i = 1}^{N}{\frac{\left\lbrack {{J_{{ex}\; p}\left( t_{i} \right)} - {J_{model}\left( t_{i} \right)}} \right\rbrack^{2}}{\left\lbrack {J_{{ex}\; p}\left( t_{i} \right)} \right\rbrack^{2}}.}}$

For reliable conversion of the time-dependent creep data into thefrequency-dependent dynamic data, the frequency range needs to belimited by the testing time of the creep measurement. If it is possibleto obtain precise experimental data over the entire range of creep timeuntil the creep compliance reaches the steady state, the exact functionof retardation spectra over the entire range of time scale also can becalculated. However, it is often not practical to obtain such data forhigh molecular weight polymers, which have very long relaxation times.The creep data only contain information within a limited range of time,so that the frequency range is limited by the duration time t_(N) of thecreep test, i.e., valid information for frequencies is in the range ofω>t_(N) ⁻¹, and the extrapolated data outside this frequency range canbe influenced by artifacts of the fittings.

For the rheological measurements involving a creep adjustment, thepolymer samples were compression molded at 182° C. for a total of 3 min.The samples were allowed to melt at a relatively low pressure for 1 minand then subjected to a high molding pressure for an additional 2 min.The molded samples were then quenched in a room temperature press, andthen 25.4 mm diameter disks were stamped out of the molded slabs for themeasurement in the rotational rheometer. The measurements were performedin parallel plates of 25 mm diameter at 190° C. using acontrolled-stress rheometer equipped with an air bearing system (PhysicaMCR-501, Anton Paar). The test chamber of the rheometer was purged withnitrogen to minimize oxidative degradation. After thermal equilibration,the specimens were squeezed between the plates to a 1.6 mm thickness,and the excess was trimmed. A total of 8 min elapsed between the timethe sample was inserted and the time the test was started. For thedynamic frequency sweep measurement, small-strain (1-10%) oscillatoryshear in the linear viscoelastic regime was applied at angularfrequencies from 0.0316 to 316 sec⁻¹. The creep test was performed for10,200 sec (170 min) to limit the overall testing time within 4 hr,since sample throughput and thermal stability were concerns. Byconverting the time dependent creep data to frequency dependent dynamicdata, the low frequency range was extended down to 10⁴ rad/sec, twoorders of magnitude lower than the frequency range of the dynamic test.The complex viscosity (|η*|) versus frequency (co) data were curvefitted using the Carreau-Yasuda model.

One of the major concerns in performing the creep test, and indeed anylong time scale measurement, was that the sample does not appreciablychange during the measurement, which may take several hours to perform.If a polymer sample is heated for long time period without properthermal stabilization (e.g., antioxidants), changes in the polymer canoccur that can have a significant effect on the rheological behavior ofthe polymer and its characterization. Polymers which are being testedshould have thermal stability for at least 4-5 hr at 190° C. undernitrogen; for example, ethylene polymers containing at least 0.4 wt. %of antioxidants were found to be stable enough to obtain valid creepadjustment data.

For the rheological measurement in the parallel plates, the specimen wassqueezed between the plates to a 1.6 mm thickness, and then the excesswas trimmed. When the sample was trimmed with large forces on onedirection, some residual stress was generated to cause the strain todrift. Therefore, performing the creep test right after sample trimmingshould be avoided, because the residual stress can affect the subsequentcreep measurement, particularly for the highly viscoelastic resinshaving long relaxation times. If the applied stress of the creep test isnot large enough, the resulting strain can be so small that the creepresults can be influenced by the artifact of the strain drifting. Inorder to minimize this effect, samples were trimmed as gently aspossible, and the creep test was conducted after 2000 sec of waitingtime, in order to allow relaxation of any residual stress.

The appropriate magnitude of applied stress σ₀ is important for reliablecreep data. The stress σ₀ must be sufficiently small such that thestrain will stay within the linear viscoelastic regime, and it must besufficiently large such that the strain signal is strong enough toprovide satisfactory resolution of data for good precision. Although notlimited thereto, a suitable applied stress was equal to the complexmodulus |G*| at a frequency of 0.01 rad/sec multiplied by 0.04.

Polymer viscosities at 0.01 sec⁻¹ (referred to as η (0.01)) and 0.001sec⁻¹ (referred to as η (0.001)) at 190° C. were determined with theAnton Paar MCR 501 rheometer using parallel-plate geometry.

The long chain branches (LCB's) per 1,000,000 total carbon atoms werecalculated using the method of Janzen and Colby (J. Mol. Struct.,485/486, 569-584 (1999)), from values of zero shear viscosity, η₀(determined from the Carreau-Yasuda model with creep adjustment,described hereinabove), and measured values of Mw (determined asdescribed above). See also U.S. Pat. No. 8,114,946; J. Phys. Chem. 1980,84, 649; and Y. Yu, D. C. Rohlfing, G. R Hawley, and P. J. DesLauriers,Polymer Preprints, 44, 49-50 (2003). These references are incorporatedherein by reference in their entirety.

Short chain branch (SCB) content and short chain branching distribution(SCBD) across the molecular weight distribution can be determined via anIR5-detected GPC system (IR5-GPC), wherein the GPC system was a PL220GPC/SEC system (Polymer Labs, an Agilent company) equipped with threeStyragel HMW-6E columns (Waters, Mass.) for polymer separation. Athermoelectric-cooled IR5 MCT detector (IR5) (Polymer Char, Spain) isconnected to the GPC columns via a hot-transfer line. Chromatographicdata are obtained from two output ports of the IR5 detector. First, theanalog signal goes from the analog output port to a digitizer beforeconnecting to Computer “A” for molecular weight determinations via theCirrus software (Polymer Labs, now an Agilent Company) and the integralcalibration method using a broad HDPE MARLEX BHB5003 resin (ChevronPhillips Chemical) as the broad molecular weight standard. The digitalsignals, on the other hand, go via a USB cable directly to Computer “B”where they are collected by a LabView data collection software providedby Polymer Char. Chromatographic conditions are set as follows: columnoven temperature of 145° C.; flowrate of 1 mL/min; injection volume of0.4 mL; and polymer concentration of about 2 mg/mL, depending on samplemolecular weight. The temperatures for both the hot-transfer line andIR5 detector sample cell are set at 150° C., while the temperature ofthe electronics of the IR5 detector is set at 60° C. Short chainbranching content is determined via an in-house method using theintensity ratio of CH₃ (I_(CH3)) to CH₂ (I_(CH2)) coupled with acalibration curve. The calibration curve is a plot of SCB content(x_(SCB)) as a function of the intensity ratio of I_(CH3)/I_(CH2). Toobtain a calibration curve, a group of polyethylene resins (no less than5) of SCB level ranging from zero to ca. 32 SCB/1,000 total carbons (SCBStandards) is used. All these SCB Standards have known SCB levels andflat SCBD profiles predetermined separately by NMR and thesolvent-gradient fractionation coupled with NMR (SGF-NMR) methods. UsingSCB calibration curves thus established, profiles of short chainbranching distribution across the molecular weight distribution areobtained for resins fractionated by the IR5-GPC system under exactly thesame chromatographic conditions as for these SCB standards. Arelationship between the intensity ratio and the elution volume isconverted into SCB distribution as a function of MWD using apredetermined SCB calibration curve (i.e., intensity ratio ofI_(CH3)/I_(CH2) vs. SCB content) and MW calibration curve (i.e.,molecular weight vs. elution time) to convert the intensity ratio ofI_(CH3)/I_(CH2) and the elution time into SCB content and the molecularweight, respectively. Although not tested, it was expected that thenumber of short chain branches (SCB) per 1000 total carbon atoms of theethylene polymer (or the base resin) at Mw (or Mz) is greater than atMn.

The oxidative induction temperature (OIT) was determined in accordancewith ASTM D3895. While not tested, it was expected that the percentelongation at break and yield strength of the ethylene polymers andpipes would be at least 500% and at least 3000 psi, respectively, whendetermined in accordance with ASTM D638. While not tested, it was alsoexpected that the Charpy ductile to brittle transition temperature forthe ethylene polymers and pipes would be below −10° C., when determinedin accordance with ASTM F2231.

Examples A-D

Table I summarizes the properties of the black pipe of Example A, andthe natural (no colorant) ethylene polymers of Examples B-C. Table IIsummarizes the properties of the base resin that was used to produce theethylene polymer of Example B (the base resins for Example A and C hadsimilar properties to that of the base resin of Example B).

The base resin for Polymer B was produced in a 30-gallon dual loopreactor system in which the first loop slurry reactor was operated at apolymerization temperature of 87° C., a pressure of 570 psig, andisobutane, 1-hexene, and ethylene feeds rates of 60 lb/hr, 1.4 lb/hr,and 31 lb/hr, respectively. Hydrogen concentration was 0.05 mol % basedon reactor contents, and triethylaluminum concentration was 67 ppm byweight of isobutane. The catalyst was a solid titanium-containingZiegler-Natta catalyst, and it was fed to the first reactor at a rate of0.002-0.0035 lb/hr. The HMW component of the base resin was produced inthe first loop slurry reactor, and constituted approximately 50 wt. % ofthe overall base resin.

The second loop slurry reactor was operated at a polymerizationtemperature of 94° C., a pressure of 575 psig, and isobutane andethylene feeds rates of 50 lb/hr and 37 lb/hr, respectively. Hydrogenconcentration was 1 mol % based on reactor contents, andtriethylaluminum concentration was 55 ppm by weight of isobutane. TheLMW component of the base resin was produced in the second loop slurryreactor, and constituted approximately 50 wt. % of the overall baseresin.

Certain polymer properties of the base resin of Example B are summarizedin Table II. The respective LMW and HMW component properties in Table IIwere determined by deconvoluting the molecular weight distribution of abase resin having similar properties to the base resins of Examples A-C.The relative amounts of the LMW and HMW components (weight percentages)in the polymer can be determined using a commercial software program(Systat Software, Inc., PEAK FIT v. 4.05). The other molecular weightparameters for the LMW and HMW components (e.g., Mn, Mw, and Mz of eachcomponent) were determined by using the deconvoluted data from the PEAKFIT program, and applying a Schulz-Flory distribution mathematicalfunction and a Gaussian peak fit, as generally described in U.S. Pat.No. 7,300,983, which is incorporated herein by reference in itsentirety. As shown in Table II, the wt. % of the HMW component was 50wt. %, the Mw of the HMW component was 520,000 g/mol, the Mw/Mn of theHMW component was 5.3, the Mw of the LMW component was 29,300 g/mol, andthe Mw/Mn of the LMW component was 5.

The ethylene polymers of Examples A-C were prepared by blending therespective base resins of Examples A-C with a masterbatch containing apolymer carrier resin and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. Theamount of peroxide groups was 125 ppm by weight of peroxide groups,based on the weight of the base resin. The blend of the base resin andperoxide masterbatch was compounded using a Kobe mixer (Example B) or atwin screw extrusion system (ZSK-300, for Examples A and C), and thenpelletized to form the ethylene polymers of Examples A-C. The propertiesof the polymers of Examples B-C are listed in Table I. For Examples B-C,the density was 0.948-0.949 g/cm³, the HLMI (I₂₁) was 6.8-7.3 g/10 min,the zero-shear viscosity (η₀) at 190° C. was 100,000-210,000 kPa-sec,the relaxation time was 1700-1900 sec, the CY-a parameter was 0.12-0.16,the number of LCB per million total carbon atoms was 8-14, the η (0.01)was 520-530 kPa-sec, the η (0.001) was 1500-1900 kPa-sec, and theaverage number of LCB per Mw (vf) was 0.21-0.31.

The ethylene polymers of Examples A-C also contained 2000 ppm of IRGANOX1010, 2000 ppm of IRGAFOS 168, 400 ppm of calcium stearate, and 400 ppmof a polymer processing aid. These additives were added to the baseresin along with the peroxide masterbatch.

The ethylene polymer of Example A was subsequently mixed with 2-3 wt. %carbon black additive and extruded at a production rate of greater than2,000 lb/hr on a 120 mm grooved feed single screw extruder with a basketdesign pipe die to produce a black pipe at a wall thickness ofapproximately 3.3 inches and an outer diameter of 24 inches. The polymerproperties of the black pipe of Example A is listed in Table I, andthese properties are generally consistent with those of the ethylenepolymers of Examples B-C.

The molecular weight distribution curve for the ethylene polymer ofExample C is illustrated in FIG. 1, and the rheology curves (viscosityversus shear rate) for the ethylene polymers of Examples A-C are shownin FIG. 2, including shear rates down to 10⁻⁴ sec⁻¹. Of particularinterest is the very high viscosity are low shear rates.

Pipe failure times of at least 1200 hr, at least 3400 hr, or at least7400 hr, under chlorinated water conditions at 90° C. and 450 psi, weredetermined in accordance with ASTM F2263-07e1. A pipe was made from theethylene polymer of Example A in a manner similar to the black pipe ofExample A, but at a 4-inch diameter. This 4-inch black pipe has afailure time of at least 6800 hr (still in testing); the additivepackage comprised 2000 ppm of phenolic antioxidant, 2000 ppm ofphosphite antioxidant, 400 ppm of acid scavenger, and 400 ppm ofprocessing aid.

Pipes were also made from ethylene polymers similar to Examples B-C, andthese 4-inch pipes have a failure time of at least 3400 hr (still intesting); the additive package comprised 3500 ppm of phenolicantioxidant, 750 ppm of phosphite antioxidant, and 400 ppm of processingaid.

Hydrostatic strengths at 23° C. or 60° C. after 100,000 hr weredetermined in accordance with ASTM D1598 and ASTM D2837. The pipesproduced as described herein (pressure tested in accordance with ASTMD1598 and analyzed in accordance with ASTM D2837) had a hydrostaticstrength of 1600 psi at 23° C. for 100,000 hr, and a hydrostaticstrength of 1000 psi at 60° C. for 100,000 hr.

Table III summarizes certain properties of the black pipe of Example A,the natural (no colorant) ethylene polymers of Examples B-C, and theblack pipe of Example D (produced in a similar manner to the black pipeof Example A). Also included in Table III are comparative Examples 1-3,which are commercially-available low slump pipe resins (blackpigmented). As shown in Table III, the relaxation time, η (0.01), and η(0.001) of Examples A-D were significantly higher than the respectiveproperties of comparative Examples 1-3.

Slump or sag during extrusion of large diameter, thick wall pipe dependson the melt strength of the resin. Besides rheology parameters (e.g.,Table III), another way to characterize the melt strength is byextruding a parison from a blow molding machine, and measuring the timethat it takes for the parison to break under its own weight.Measurements were performed on a Kautex KB-25 accumulator head blowmolder with a 3.15″ grooved feed single screw extruder to convey andpush the melt through the die into the mold, 32″ wide and 30.315″ long.Under the same set of processing conditions of die gap and melttemperature, it took much longer for the parison extruded from ethylenepolymers of this invention to break off under its own weight (parisonsag time) than comparative polymers. Comparative Examples 2-3 hadparison sag times (before break) of approximately 25 seconds, whereaspolymers similar to Example C and to the polymer used to make the blackpipe of Example A had parison sag times (before break) of approximately50 seconds. Surprisingly, the parison sag times for ethylene polymers ofthis invention were twice that of comparative low slump pipe resins.

TABLE I Examples A-C-Pipe and ethylene polymer properties Example A B CDensity (g/cc) — 0.949 0.948 HLMI (g/10 min) — 6.8-7.3 7.1 I₅ (g/10 min)— — 0.25 η₀ (kPa-sec) 55,200 101,000 206,000 τ_(η) (sec) 522 1840 1720CY-a 0.145 0.152 0.122 LCB (per million) 14 8 14 LCB/Mw (vf) 0.27 0.210.31 η (0.01) (kPa-sec) 527 527 525 η (0.001) (kPa-sec) 1410 1820 1530Mw (kg/mol) 259 358 289 Mw/Mn 21 35 18 OIT (° C.) — — 247

TABLE II Example B-Base resin properties (reactor fluff) Example BDensity (g/cc) 0.9464 HLMI (g/10 min) 12.61 Ratio of HLMI/I₅ 31 Mn(kg/mol) 9 Mw (kg/mol) 345 Mz (kg/mol) 2303 Mw/Mn 38 Mz/Mw 6.7 HighMolecular Weight (HMW) Component Wt. % 50 HLMI₂₇₅ (g/10 min) 0.57Density (g/cc) 0.928 Mn (kg/mol) 98 Mw (kg/mol) 520 Mz (kg/mol) 1784Mw/Mn 5.3 Mz/Mw 3.4 Low Molecular Weight (LMW) Component Mn (kg/mol) 5.8Mw (kg/mol) 29.3 Mz (kg/mol) 78.2 Mw/Mn 5.0 Mz/Mw 2.7

TABLE III Examples A-D and Comparative Examples 1-3 - Pipe and ethylenepolymer properties Example A B C D 1 2 3 η₀ (kPa-sec) 55,200 101,000206,000 33,800 1,500 51,500 40,500 τ_(η) (sec) 522 1840 1720 333 11 200166 CY-a 0.145 0.152 0.122 0.157 0.233 0.120 0.124 η (0.01) (kPa-sec)527 527 525 529 288 334 330 η (0.001) (kPa-sec) 1410 1820 1530 1380 520830 820

The invention is described above with reference to numerous aspects andspecific examples. Many variations will suggest themselves to thoseskilled in the art in light of the above detailed description. All suchobvious variations are within the full intended scope of the appendedclaims. Other aspects of the invention can include, but are not limitedto, the following (aspects are described as “comprising” but,alternatively, can “consist essentially of” or “consist of”):

Aspect 1. An ethylene polymer having (or characterized by):

a density of at least about 0.94 g/cm³;

a HLMI (I₂₁) in a range from about 4 to about 20 g/10 min;

a zero-shear viscosity (η₀) at 190° C. in a range from about 20,000 toabout 400,000 kPa-sec; and

a relaxation time (τ_(η)) at 190° C. in a range from about 225 to about3000 sec.

Aspect 2. The polymer defined in aspect 1, wherein the ethylene polymerhas a density in any range disclosed herein, e.g., from about 0.94 toabout 0.96, from about 0.94 to about 0.955, from about 0.945 to about0.96, from about 0.942 to about 0.952, from about 0.94 to about 0.95g/cm³, etc.

Aspect 3. The polymer defined in aspect 1 or 2, wherein the ethylenepolymer has a HLMI (I₂₁) in any range disclosed herein, e.g., from about4 to about 18, from about 5 to about 15, from about 6 to about 16, fromabout 6 to about 14 g/10 min, etc.

Aspect 4. The polymer defined in any one of aspects 1-3, wherein theethylene polymer has a zero-shear viscosity (η₀) at 190° C. in any rangedisclosed herein, e.g., from about 30,000 to about 300,000, from about30,000 to about 275,000, from about 20,000 to about 250,000, from about25,000 to about 250,000, from about 25,000 to about 230,000, from about30,000 to about 215,000 kPa-sec, etc.

Aspect 5. The polymer defined in any one of aspects 1-4, wherein theethylene polymer has a relaxation time in any range disclosed herein,e.g., from about 250 to about 2500 sec, from about 275 to about 2000sec, from about 300 to about 2500 sec, from about 300 to about 2000 sec,etc.

Aspect 6. The polymer defined in any one of aspects 1-5, wherein theethylene polymer has a CY-a parameter at 190° C. in any range disclosedherein, e.g., from about 0.06 to about 0.25, from about 0.09 to about0.2, from about 0.1 to about 0.18, from about 0.1 to about 0.16, fromabout 0.12 to about 0.15, etc.

Aspect 7. The polymer defined in any one of aspects 1-6, wherein theethylene polymer has a number of long chain branches (LCB) per milliontotal carbon atoms in any range disclosed herein, e.g., from about 5 toabout 50, from about 5 to about 35, from about 5 to about 32, from about6 to about 28, from about 6 to about 26, from about 7 to about 20 LCB,etc.

Aspect 8. The polymer defined in any one of aspects 1-7, wherein theethylene polymer has a viscosity at 0.01 sec⁻¹ {η (0.01)} at 190° C. inany range disclosed herein, e.g., from about 300 to about 800, fromabout 400 to about 700, from about 450 to about 750, from about 500 toabout 750, from about 500 to about 650 kPa-sec, etc.

Aspect 9. The polymer defined in any one of aspects 1-8, wherein theethylene polymer has a viscosity at 0.001 sec⁻¹ {η (0.001)} at 190° C.in any range disclosed herein, e.g., from about 800 to about 3000, fromabout 900 to about 2800, from about 1000 to about 2600, from about 1000to about 2300, from about 1200 to about 2100, from about 1300 to about1900 kPa-sec, etc.

Aspect 10. The polymer defined in any one of aspects 1-9, wherein theethylene polymer has a reverse comonomer distribution, e.g., the numberof short chain branches (SCB) per 1000 total carbon atoms of the polymerat Mw (or Mz) is greater than at Mn.

Aspect 11. The polymer defined in any one of aspects 1-10, wherein theethylene polymer has a 15 in any range disclosed herein, e.g., fromabout 0.02 to about 0.3, from about 0.03 to about 0.25, from about 0.05to about 0.18, from about 0.06 to about 0.15 g/10 min, etc.

Aspect 12. The polymer defined in any one of aspects 1-11, wherein theethylene polymer has an average number of LCB per Mw (vf) in any rangedisclosed herein, e.g., from about 0.15 to about 0.51, from about 0.16to about 0.43, from about 0.18 to about 0.37, etc.

Aspect 13. The polymer defined in any one of aspects 1-12, wherein theethylene polymer has a ratio of Mw/Mn in any range disclosed herein,e.g., from about 13 to about 38, from about 14 to about 39, from about16 to about 37, from about 18 to about 35, etc., and/or a Mw in anyrange disclosed herein, e.g., from about 220,000 to about 500,000, fromabout 210,000 to about 400,000, from about 230,000 to about 380,000,from about 250,000 to about 360,000 g/mol, etc.

Aspect 14. The polymer defined in any one of aspects 1-13, wherein theethylene polymer comprises an ethylene/α-olefin copolymer.

Aspect 15. The polymer defined in any one of aspects 1-13, wherein theethylene polymer comprises an ethylene homopolymer, an ethylene/1-butenecopolymer, an ethylene/1-hexene copolymer, an ethylene/1-octenecopolymer, or a combination thereof.

Aspect 16. The polymer defined in any one of aspects 1-15, wherein theethylene polymer further comprises at least one additive selected froman antioxidant, an acid scavenger, an antiblock additive, a slipadditive, a colorant, a filler, a processing aid, a UV inhibitor, etc.,or any combination thereof.

Aspect 17. The polymer defined in any one of aspects 1-16, wherein theethylene polymer further comprises an amount of carbon black in anyrange disclosed herein, e.g., from about 0.5 to about 5 wt. %, fromabout 1 to about 4 wt. %, from about 2 to about 3 wt. %, etc.

Aspect 18. The polymer defined in any one of aspects 1-17, wherein theethylene polymer is further characterized by less than 300 gels/ft², forgels of at least 200 microns, when extruded at a specific energy of lessthan 0.25 kW-hr/kg.

Aspect 19. The polymer defined in any one of aspects 1-18, wherein theethylene polymer is capable of producing a pipe having at least a24-inch diameter and at least a 2-inch wall thickness.

Aspect 20. The polymer defined in any one of aspects 1-19, wherein theethylene polymer is further characterized by a percent elongation atbreak in any range disclosed herein, e.g., from about 450 to about 850%,from about 500 to about 800%, from about 550 to about 750%, etc.

Aspect 21. The polymer defined in any one of aspects 1-20, wherein theethylene polymer is further characterized by a yield strength in anyrange disclosed herein, e.g., from about 3000 to about 5000 psi, fromabout 3500 to about 4500 psi, from about 3500 to about 4000 psi, etc.

Aspect 22. The polymer defined in any one of aspects 1-21, wherein theethylene polymer is further characterized by an oxidative inductiontemperature (OIT) in any range disclosed herein, e.g., at least about200° C., at least about 220° C., at least about 240° C., etc.

Aspect 23. The polymer defined in any one of aspects 1-22, wherein theethylene polymer is further characterized by a Charpy ductile to brittletransition temperature in any range disclosed herein, e.g., from about−35 to about −5° C., from about −30 to about −10° C., etc.

Aspect 24. An article of manufacture comprising the ethylene polymerdefined in any one of aspects 1-23.

Aspect 25. A pipe comprising the ethylene polymer defined in any one ofaspects 1-23.

Aspect 26. A pipe comprising the ethylene polymer defined in any one ofaspects 1-23 and an amount of carbon black in any range disclosedherein, e.g., from about 0.5 to about 5 wt. %, from about 1 to about 4wt. %, from about 2 to about 3 wt. %, etc.

Aspect 27. The pipe defined in aspect 25 or 26, wherein the pipe has thepolymer properties defined in any one of aspects 1-23.

Aspect 28. The pipe defined in any one of aspects 25-27, wherein thepipe has a diameter of at least 24 inches and a wall thickness of atleast 2 inches.

Aspect 29. The pipe defined in any one of aspects 25-28, wherein thepipe has a hydrostatic strength of 1600 psi at 23° C. for 100,000 hrand/or a hydrostatic strength of 1000 psi at 60° C. for 100,000 hr, inaccordance with ASTM D1598 and ASTM D2837.

Aspect 30. A base resin having (or characterized by):

a density of at least about 0.94 g/cm³;

a HLMI (I₂₁) in a range from about 4 to about 25 g/10 min;

a Mw in a range from about 200,000 to about 500,000 g/mol; and

a ratio of Mw/Mn in a range from about 12 to about 40.

Aspect 31. The base resin defined in aspect 30, wherein the base resinhas a density in any range disclosed herein, e.g., from about 0.94 toabout 0.955, from about 0.945 to about 0.96, from about 0.942 to about0.952, from about 0.94 to about 0.95 g/cm³, etc.

Aspect 32. The base resin defined in aspect 30 or 31, wherein the baseresin has a ratio of Mw/Mn in any range disclosed herein, e.g., fromabout 13 to about 38, from about 14 to about 39, from about 16 to about37, from about 18 to about 35, etc.

Aspect 33. The base resin defined in any one of aspects 30-32, whereinthe base resin has a Mw in any range disclosed herein, e.g., from about220,000 to about 500,000, from about 210,000 to about 400,000, fromabout 230,000 to about 380,000, from about 250,000 to about 360,000g/mol, etc.

Aspect 34. The base resin defined in any one of aspects 30-33, whereinthe base resin has a Mn in any range disclosed herein, e.g., from about8,000 to about 20,000, from about 9,000 to about 8,000, from about10,000 to about 16,000 g/mol, etc.

Aspect 35. The base resin defined in any one of aspects 30-34, whereinthe base resin has a Mz in any range disclosed herein, e.g., from about1,000,000 to about 2,500,000, from about 1,000,000 to about 2,300,000,from about 1,100,000 to about 2,200,000 g/mol, etc.

Aspect 36. The base resin defined in any one of aspects 30-35, whereinthe base resin has a reverse comonomer distribution, e.g., the number ofshort chain branches (SCB) per 1000 total carbon atoms of the polymer atMw (or Mz) is greater than at Mn.

Aspect 37. The base resin defined in any one of aspects 30-36, whereinthe base resin has a HLMI (I₂₁) in any range disclosed herein, e.g.,from about 6 to about 20, from about 7 to about 18, from about 8 toabout 16 g/10 min, etc.

Aspect 38. The base resin defined in any one of aspects 30-37, whereinthe base resin has a ratio of HLMI/I₅ in any range disclosed herein,e.g., from about 20 to about 45, from about 25 to about 40, from about29 to about 35, etc.

Aspect 39. The base resin defined in any one of aspects 30-38, whereinthe base resin comprises an ethylene/α-olefin copolymer.

Aspect 40. The base resin defined in any one of aspects 30-38, whereinthe base resin comprises an ethylene homopolymer, an ethylene/1-butenecopolymer, an ethylene/1-hexene copolymer, an ethylene/1-octenecopolymer, or a combination thereof.

Aspect 41. The base resin defined in any one of aspects 30-38, whereinthe base resin comprises an ethylene/1-hexene copolymer.

Aspect 42. The base resin defined in any one of aspects 30-41, whereinthe base resin further comprises at least one additive selected from anantioxidant, an acid scavenger, an antiblock additive, a slip additive,a colorant, a filler, a processing aid, a UV inhibitor, etc., or anycombination thereof.

Aspect 43. The base resin defined in any one of aspects 30-42, whereinthe base resin comprises a higher molecular weight component and a lowermolecular weight component.

Aspect 44. The base resin defined in aspect 43, wherein an amount of thehigher molecular weight component, based on the total polymer, is in anyrange of weight percentages disclosed herein, e.g., from about 35 toabout 65 wt. %, from about 40 to about 60 wt. %, from about 45 to about55 wt. %, etc.

Aspect 45. The base resin defined in any one of aspects 43-44, whereinthe higher molecular weight component has a HLMI₂₇₅ (I₂₁ using a 2.75 mmdiameter capillary) in any range disclosed herein, e.g., from about 0.2to about 1, from about 0.3 to about 0.9, from about 0.4 to about 0.8g/10 min, etc.

Aspect 46. The base resin defined in any one of aspects 43-45, whereinthe higher molecular weight component has a density in any rangedisclosed herein, e.g., from about 0.915 to about 0.94, from about 0.92to about 0.94, from about 0.92 to about 0.93, from about 0.922 to about0.932 g/cm³, etc.

Aspect 47. The base resin defined in any one of aspects 43-46, whereinthe higher molecular weight component has a ratio of Mw/Mn in any rangedisclosed herein, e.g., from about 4 to about 8, from about 4 to about7, from about 4.5 to about 6.5, from about 5 to about 6, etc.

Aspect 48. The base resin defined in any one of aspects 43-47, whereinthe higher molecular weight component has a Mn in any range disclosedherein, e.g., from about 80,000 to about 120,000, from about 90,000 toabout 110,000 g/mol, etc.

Aspect 49. The base resin defined in any one of aspects 43-48, whereinthe higher molecular weight component has a Mw in any range disclosedherein, e.g., from about 425,000 to about 650,000, from about 500,000 toabout 600,000 g/mol, etc.

Aspect 50. The base resin defined in any one of aspects 43-49, whereinthe higher molecular weight component has a Mz in any range disclosedherein, e.g., from about 1,500,000 to about 2,500,000, from about1,600,000 to about 2,000,000 g/mol, etc.

Aspect 51. The base resin defined in any one of aspects 43-50, whereinthe lower molecular weight component has a ratio of Mw/Mn in any rangedisclosed herein, e.g., from about 4 to about 8, from about 4 to about7, from about 4.5 to about 6.5, from about 4.5 to about 6, etc.

Aspect 52. The base resin defined in any one of aspects 43-51, whereinthe lower molecular weight component has a Mn in any range disclosedherein, e.g., from about 4,000 to about 8,000, from about 5,000 to about7,000 g/mol, etc.

Aspect 53. The base resin defined in any one of aspects 43-52, whereinthe lower molecular weight component has a Mw in any range disclosedherein, e.g., from about 20,000 to about 40,000, from about 25,000 toabout 35,000 g/mol, etc.

Aspect 54. The base resin defined in any one of aspects 43-53, whereinthe lower molecular weight component has a Mz in any range disclosedherein, e.g., from about 50,000 to about 110,000, from about 65,000 toabout 95,000 g/mol, etc.

Aspect 55. The base resin defined in any one of aspects 30-54, whereinthe base resin is produced using a Ziegler-Natta catalyst system.

Aspect 56. The base resin defined in any one of aspects 30-55, whereinthe base resin is produced in any reactor disclosed herein, e.g., aslurry reactor, a gas-phase reactor, a solution reactor, a multi-zonecirculating reactor (a single reactor with at least two reaction zones,with different reaction conditions in each reaction zone), etc., as wellas multi-reactor combinations thereof.

Aspect 57. The base resin defined in any one of aspects 30-56, whereinthe base resin is produced in a dual loop slurry reactor.

Aspect 58. A process for preparing an ethylene polymer, the processcomprising contacting the base resin defined in any one of aspects 30-57with a peroxide compound to produce the ethylene polymer defined in anyone of aspects 1-23.

Aspect 59. The process defined in aspect 58, wherein the contacting stepis conducted at a temperature sufficient to generate peroxide groups atabout 60 to about 200 ppm, from about 75 to about 175 ppm, from about100 to about 150 ppm, etc., of peroxide groups, based on the weight ofthe base resin.

Aspect 60. The process defined in aspect 58 or 59, wherein thecontacting step comprises melt processing a blend (or mixture) of thebase resin and the peroxide compound at any melt processing temperaturedisclosed herein, e.g., in a range from about 120 to about 300° C., in arange from about 150 to about 250° C., in a range from about 175 toabout 225° C., etc.

Aspect 61. The process defined in aspect 60, wherein the melt processingis performed in a twin screw extrusion system.

Aspect 62. The process defined in aspect 60, wherein the melt processingis performed in a single screw extrusion system.

Aspect 63. The process defined in any one of aspects 58-62, wherein theperoxide compound comprises any suitable peroxide compound, or anyperoxide compound disclosed herein, e.g.,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, t-butylcumyl peroxide, n-butyl-4,4′-di(t-butylperoxy)valerate, etc., or anycombination thereof.

Aspect 64. A method of making a pipe comprising an ethylene polymer, themethod comprising melt processing the ethylene polymer defined in anyone of aspects 1-23 through a pipe die to form the pipe.

Aspect 65. The method defined in aspect 64, wherein the method comprisesmelt processing the ethylene polymer and at least one additive throughthe die.

Aspect 66. The method defined in aspect 65, wherein the additivecomprises an antioxidant, an acid scavenger, an antiblock additive, aslip additive, a colorant, a filler, a processing aid, a UV inhibitor,or any combination thereof.

Aspect 67. The method defined in any one of aspects 64-66, wherein thepipe has a thickness in any range disclosed herein, e.g., from about 0.1to about 5 inches, from about 0.5 to about 5 inches, from about 1 toabout 4 inches, from about 2 to about 3 inches, etc.

Aspect 68. The method defined in any one of aspects 64-67, wherein thepipe has an outer diameter in any range disclosed herein, e.g., fromabout ¼ to about 100 inches, from about 12 to about 100 inches, fromabout 24 to about 63 inches, etc.

Aspect 69. The method defined in any one of aspects 64-68, wherein thepipe has a failure time of at least 1200 hr, at least 3400 hr, at least7400 hr, etc., under chlorinated water conditions at 90° C. and 450 psi,in accordance with ASTM F2263-07e1.

Aspect 70. A pipe formed by the method defined in any one of aspects64-69.

Aspect 71. A pipe formed by the method defined in any one of aspects64-69, wherein the pipe is defined in any one of aspects 25-29.

We claim:
 1. A process for preparing an ethylene polymer, the processcomprising: contacting a base resin with a peroxide compound to producethe ethylene polymer, wherein the ethylene polymer is characterized by:a density of at least about 0.94 g/cm³; a HLMI (I₂₁) in a range fromabout 4 to about 20 g/10 min; a zero-shear viscosity (η₀) at 190° C. ina range from about 20,000 to about 400,000 kPa-sec; and a relaxationtime (τ_(η)) at 190° C. in a range from about 225 to about 3000 sec. 2.The process of claim 1, wherein the base resin is characterized by: adensity of at least about 0.94 g/cm³; a HLMI (I₂₁) in a range from about4 to about 25 g/10 min; a Mw in a range from about 200,000 to about500,000 g/mol; and a ratio of Mw/Mn in a range from about 12 to about40.
 3. The process of claim 2, wherein: the base resin has: a Mn in arange from about 8,000 to about 20,000 g/mol; a Mz in a range from about1,000,000 to about 2,500,000 g/mol; and a ratio of HLMI/I₅ in a rangefrom about 20 to about 45; and the base resin comprises an ethylenehomopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexenecopolymer, an ethylene/1-octene copolymer, or a combination thereof. 4.The process of claim 3, wherein: the base resin is produced using aZiegler-Natta catalyst system; and the base resin comprises a highermolecular weight component and a lower molecular weight component;wherein: the higher molecular weight component is characterized by: adensity in a range from about 0.915 to about 0.94 g/cm³; a ratio ofMw/Mn in a range from about 4 to about 8; and a Mw in a range from about425,000 to about 650,000 g/mol; and the lower molecular weight componentis characterized by: a ratio of Mw/Mn in a range from about 4 to about8; and a Mw in a range from about 20,000 to about 40,000 g/mol.
 5. Theprocess of claim 1, wherein an amount of the peroxide compound is fromabout 60 to about 200 ppm by weight of peroxide groups, based on theweight of the base resin.
 6. The process of claim 1, wherein the step ofcontacting the base resin with the peroxide compound comprises meltprocessing a mixture of the base resin and the peroxide compound in atwin screw extrusion system.
 7. The process of claim 1, wherein: thestep of contacting the base resin with the peroxide compound comprisesmelt processing a mixture of the base resin, the peroxide compound, andan additive at a melt processing temperature in a range from about 120to about 300° C.; and the additive comprises an antioxidant, an acidscavenger, an antiblock additive, a slip additive, a colorant, a filler,a processing aid, a UV inhibitor, or any combination thereof.
 8. Anethylene polymer having: a density of at least about 0.94 g/cm³; a HLMI(I₂₁) in a range from about 4 to about 20 g/10 min; a zero-shearviscosity (η₀) at 190° C. in a range from about 20,000 to about 400,000kPa-sec; and a relaxation time (τ_(η)) at 190° C. in a range from about225 to about 3000 sec.
 9. An article of manufacture comprising thepolymer of claim
 8. 10. The polymer of claim 8, wherein: the density isin a range from about 0.94 to about 0.96 g/cm³; the HLMI (I₂₁) is in arange from about 4 to about 18 g/10 min; the zero-shear viscosity (η₀)at 190° C. is in a range from about 30,000 to about 300,000 kPa-sec; andthe relaxation time (τ_(η)) at 190° C. is in a range from about 250 toabout 2500 sec.
 11. A pipe comprising the polymer of claim
 10. 12. Thepolymer of claim 10, wherein the ethylene polymer has: a CY-a parameterat 190° C. in a range from about 0.06 to about 0.25; a number of longchain branches (LCB) in a range from about 5 to about 50 LCB per milliontotal carbon atoms; a viscosity at 0.01 sec⁻¹ at 190° C. in a range fromabout 300 to about 800 kPa-sec; and a viscosity at 0.001 sec⁻¹ at 190°C. in a range from about 800 to about 3000 kPa-sec.
 13. The polymer ofclaim 12, wherein: the ethylene polymer comprises an ethylene/1-butenecopolymer, an ethylene/1-hexene copolymer, an ethylene/1-octenecopolymer, an ethylene homopolymer, or a combination thereof; and theethylene polymer further comprises an additive selected from anantioxidant, an acid scavenger, an antiblock additive, a slip additive,a colorant, a filler, a processing aid, a UV inhibitor, or anycombination thereof.
 14. The polymer of claim 13, wherein: the CY-aparameter at 190° C. is in a range from about 0.1 to about 0.18; thenumber of long chain branches (LCB) is in a range from about 7 to about20 LCB per million total carbon atoms; the viscosity at 0.01 sec⁻¹ at190° C. is in a range from about 450 to about 750 kPa-sec; and theviscosity at 0.001 sec⁻¹ at 190° C. is in a range from about 1200 toabout 2100 kPa-sec.
 15. A pipe comprising: an ethylene polymercharacterized by a density of at least about 0.94 g/cm³, a HLMI (I₂₁) ina range from about 4 to about 20 g/10 min, a zero-shear viscosity (η₀)at 190° C. in a range from about 20,000 to about 400,000 kPa-sec, and arelaxation time (τ_(η)) at 190° C. in a range from about 225 to about3000 sec; and an additive selected from an antioxidant, an acidscavenger, an antiblock additive, a slip additive, a colorant, a filler,a processing aid, a UV inhibitor, or any combination thereof.
 16. Thepipe of claim 15, wherein the pipe comprises a colorant, and thecolorant comprises carbon black.
 17. The pipe of claim 15, wherein thepipe comprises: from about 1000 ppm to about 4500 ppm of a phenolicantioxidant; and from about 250 ppm to about 4000 ppm of a phosphiteantioxidant.
 18. The pipe of claim 17, wherein: the pipe has a thicknessin a range from about 0.5 to about 5 inches; the pipe has an outerdiameter in a range from about 12 to about 100 inches; and the pipecomprises from about 250 ppm to about 800 ppm of an acid scavenger, andfrom about 300 ppm to about 600 ppm of a processing aid.
 19. The pipe ofclaim 15, wherein the pipe is characterized by: a failure time of atleast 1200 hr under chlorinated water conditions at 90° C. and 450 psi;a failure time of at least 3400 hr under chlorinated water conditions at90° C. and 450 psi; or a failure time of at least 7400 hr underchlorinated water conditions at 90° C. and 450 psi; or any combinationthereof.
 20. The pipe of claim 15, wherein the pipe is produced by aprocess that comprises melt processing the ethylene polymer and theadditive through a pipe die to form the pipe, wherein the ethylenepolymer comprises an ethylene/α-olefin copolymer.